GB2242245A

GB2242245A - A braking system

Info

Publication number: GB2242245A
Application number: GB9104114A
Authority: GB
Inventors: Karl-Heinz Willmann; Wolf-Dieter Jonner
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1990-03-23
Filing date: 1991-02-27
Publication date: 1991-09-25
Also published as: JPH04221265A; DE4009379A1; GB9104114D0

Abstract

A braking system has a master brake cylinder (1), which is connected by way of brake lines (7, 10) to wheel brake cylinders (5, 6, 11, 12), a regulating valve (8, 13) and, for the wheel cylinders, shut-off valves (9, 16, 17), being disposed in each master brake line for anti-skid control and a line (24) branches from the master brake line beyond the regulating valve to an accumulator (26, 33), to which is connected a return pump (28, 35), which is connected by way of a return line (30) back to the master brake line beyond the regulating valve. The accumulator, which may be of a spring-loaded or active type, takes up brake fluid during anti-skid control and the pump provides for further pressure reduction when the accumulator is full. The regulating valve (8, 13) is closed to isolate the master cylinder. <IMAGE>

Description

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DESCRIPTION A BRAKING SYSTE

The present invention relates to a braking system of the type having a regulating valve and shut off valves disposed for anti-skid control in a master brake line extending between a master brake cylinder and wheel brake cylinders.

Such braking systems are adequately known and are described in many publications. By way of example, reference is made to "Bosch Technische Berichte", February 1982, ISSN 0006-789X, in which the so-called ABS 2S anti-skid system is described on page 17.

In this known system, an undamped reactive effect of the anti-skid control takes place on the brake pedal, wherein this reactive effect is experienced by the driver as unpleasant. In DE-OS 31 07 963, a braking system is described in which a total suppression of the reactive effect is effected. A hydraulic tank removes brake fluid by way of a control valve from the wheel cylinders, resulting in a drop in brake pressure. This brake fluid is withdrawn by way of a fluid pump from the hydraulic tank into an accumulator. However, this arrangement has the disadvantage that the return pump is operating against a high-pressure accumulator, wherein the corresponding -2accumulator chamber must hold the entire circuit volume. This leads to problems with regard to safety. Furthermore, pressure reduction is limited by the spring force of the accumulator, that is, reduction to very small pressure values of for example 0.5-1 bar, is not possible.

In accordance with the present invention, there is provided a braking system comprising a master brake cylinder connected by way of a master brake line to wheel brake cylinders, a regulating valve and, for the wheel brake cylinders, a shut-off valve, disposed in the master brake line for anti-skid control, wherein a line branches off from the master brake line beyond the regulating valve to an accumulator, to which is connected a return pump, which is connected by way of a return line to the master brake line also beyond the regulating valve.

In contrast to the prior art, the present invention has the advantage that, in the event of a desired pressure reduction, the accumulator contains the brake fluid and can be emptied in a controlled manner or as required by means of a return pump. This return pump may at the same time in turn carry out a pressure reduction in the wheel brake cylinders.

Beyond the regulating valve, a line, which in the event of an anti-skid control operation ensures that 1 1 -3the master brake circuit is closed with respect to the master brake cylinder, branches from the master brake line of each individual brake circuit. This line leads to an accumulator, from which brake fluid is in turn removed by means of a return pump and fed back into the brake circuit. that is into the master brake line, beyond the above-mentioned regulating valve. There is therefore no direct return of brake fluid into the master brake cylinder, such that there is no reactive effect on the pedal pressure of the driver. A so-called internal regulation inside the brake circuit takes place.

The line upstream of the accumulator may contain at least one reduction valve, which permits a closed position and an open position in one direction only, namely in the direction of the accumulator. As a result, this prevents the accumulator being filled by brake pressure, even in the event of normal braking without anti-skid control.

In a first embodiment, the accumulator may be a so-called active accumulator. that is, a corresponding accumulator piston, which may push stored brake fluid out again, is mounted therein. The way in which the displacement is effected is of subsidiary importance; it may be carried out by means of a magnetic, electromotive, hydraulic or pneumatic drive.

If a pressure reduction is desired in this embodiment, the corresponding reduction valve opens, although the accumulator is not activated. That is. the accumulator may in this case be filled with brake fluid through the reduction in pressure in the wheel brake cylinders, wherein the accumulator piston correspondingly yields.

If, in turn, a pressure build-up is desired in the wheel brake cylinders or a return'takes place, that is an emptying of the accumulator, this accumulator is activated and the accumulator piston presses out brake fluid, wherein, however, the reduction valve is closed. This pressed-out brake fluid is available upstream of the return pump and is conveyed by it back into the master brake line, thus supplying the wheel brake cylinders with corresponding brake fluid.

In a further embodiment. the corresponding return pump is self-priming, as a result of which there is no active accumulator. However, in this case a corresponding build-up valve, which has a closed position and an open position, may be disposed between the accumulator and the return pump. In this case, the accumulator piston is not under pressure, but rather brake fluid is, in the event of a desired pressure build-up, sucked by the return pump itself out of the accumulator and fed into the master brake 1 line. This continues until the accumulator volume is sufficient for pressure modulation. The brake pedal remains still for this period. The return pump delivers only against the pressure in the wheel brake cylinder and not against the pressure in the master brake cylinder, as a result of which noise is substantially reduced. Furthermore, as a result of this arrangement, the pressure in the wheel brake cylinders can be reduced to 0 bar, since the accumulator piston is free-floating.

In a further embodiment of the invention, the accumulator piston is spring-loaded. Complete pressure reduction in the wheel brake cylinders cannot be achieved by this, but relatively low values of 0.51 bar can be achieved. This of course depends upon the spring pressure itself.

An accumulator equipped in this way does however have the advantage that the return pump does not have to be self-priming, but that brake fluid to be delivered back is available upstream of the return pump through the spring-loaded accumulator piston. In this case, it does however appear necessary to provide a non-return valve in addition to the corresponding reduction valves, so that there is no return of brake fluid by way of the reduction valve to the wheel brake cylinder when the reduction valves are open and the accumulator is full.

Furthermore. a pressure-limiting valve is provided in a bypass, so that excess pump delivery volume, which is not contained by the wheel brake cylinders, can be delivered back into the accumulator chamber.

Preferably, a damping chamber should also be provided in the return line, which chamber serves to compensate pressure fluctuations in the return line.

There may a plurality of said master brake lines. Also, a plurality of shut-off valves may be provided in the or each master brake line.

By way of example only, specific embodiments of the present invention will now be described, with reference to the accompanying drawings, in which:Fig. 1 is a block diagram of an embodiment of a braking system according to the invention; Fig. 2 is a block diagram of a further embodiment of a braking system according to Fig. 1; and Fig. 3 is a block diagram of a further embodiment of a braking system according to the invention.

A braking system according to the invention has, as in Fig. 1, a master brake cylinder 1, which may be provided with an additional brake force booster and is of a conventional type. Brake pressure exerted on a brake pedal 3 is transmitted to the master brake cylinder 1 by way of a piston rod 2 leading out of master brake cylinder 1. Inside the master brake cylinder 1, there are known brake pressure chambers, from which, in the event of the application of pressure, brake fluid can pass into two brake circuits 1 and IT. The braking system is supplied with brake fluid from a corresponding supply tank 4, from which brake fluid can pass into the brake chambers.

Two wheel brake cylinders 5 and 6 of the lefthand and right-hand rear wheels are supplied with brake fluid by way of the brake circuit I. To do this, however, this brake fluid must flow in a master brake line 7 through a first regulating valve 8 and then a shut-off valve 9. The two valves 8 and 9 are preferably in the form of solenoid valves and have an open and a closed position. In the event of a normal braking operation, the two valves 8 and 9 are switched into the open position, such that, in the event of pressure reduction in the master brake cylinder 1, brake fluid can pass to the wheel brake cylinders 5 and 6.

A regulating valve 13 is also disposed in a master brake line 10 of the brake circuit II, which leads to wheel brake cylinders 11 and 12 of the lefthand and right-hand front wheels. Beyond this regulating valve 13, however, the master brake line -8branches into a branch line 14 and a branch line 15. wherein each of these branch lines 14 and 15 contains a shut-off valve 16 or 17 respectively. In this case, too, the valves 13, 16 or 17 are in the form of solenoid valves and have an open position and a closed position. During normal braking operation, the valves 13, 16 and 17 are switched to open.

Both the valves 8 and 9 of the rear axle brake circuit and the valves 13, 16 and 17 of the front axle brake circuit can be bridged by a return line 18 or 19 respectively. Non-return valves 20, 21 and 22 are disposed in these return lines 18 and 19, wherein one non-return valve 20 is sufficient for the wheel brake cylinders 5 and 6 of the rear axle brake circuit. In the event of cancellation of a brake pressure in the master brake cylinder 1, brake pressure in the wheel brake cylinders 5, 6 or 11 and 12 can be directly reduced by way of these non-return valves 20, 21 or 22 bypassing the valves 8 and 9 or 13, 16 and 17.

It is not shown that the regulating valves 8, 9 or 13, 16 and 17 are connected to a corresponding control unit for the braking system. This control unit receives pulses from wheel sensors 23, by way of which, for example, the locking of a wheel can be established. As soon as locking is indicated, an anti-skid control operation takes place, control -gelements being provided in each brake circuit I and II for this. In the brake circuit II, a line 24, which is connected by way of a reduction valve 25 to an accumulator 26, branches off between the regulating valve 13 and the shut-off valve 16. The reduction valve 25 is also a solenoid valve, which has a closed position and a one-way open position.

The accumulator 26 serves to contain brake fluid in the event of pressure reduction at the wheel brake cylinders 11 or 12. In the present embodiment, it also has a switching device 27, which indicates when the accumulator 26 has reached a pre-determined degree of filling. For the corresponding control uniti a signal from this switch 27 indicates that the accumulator 26 must be emptied, since it cannot take in any further brake fluid. The accumulator 26 is then emptied by way of a self-priming return pump 28, wherein the connection between the accumulator 26 and the return pump 28 can still be broken by a build-up valve 29. This build-up valve 29 is also in turn preferably a solenoid valve and has an open position and a closed position.

The return pump 28 is directly connected to the master brake line 10 between the regulating valve 13 and the shut-off valve 16 by means of the return line 30. A damper chamber 31 is provided to reduce noise.

In a comparable arrangement, brake circuit I also has a pressurereduction or pressure build-up arrangement, which comprises a reduction valve 32, an accumulator 33, a build-up valve 34, a return pump 35 and a damper chamber 36.

As soon as a wheel sensor 23 indicates locking of a wheel, an anti-skid control operation takes place. To do this, the connection between the master brake cylinder 1 and the respective wheel brake cylinder 5, 6, 11 or 12 is broken by the regulating valve 8. Furthermore, the return pump 28 or 35 starts up.

If, for example, the anti-skid control operation is carried out at the right-hand front wheel, the shut-off valve 16 for the wheel brake cylinder 11 is also closed for the left-hand front wheel, whereas the shut-off valve 17 for the wheel brake cylinder 12 of the right-hand front wheel is opened. At the same time, the reduction valve 25 is also opened, such that a pressure reduction takes place by way of the branch line 15 and the line 24 to the accumulator 26. The excess brake fluid volume in the wheel brake cylinder 12 of the right-hand front wheel is thus contained in the accumulator 26.

As soon as it is recognised by way of the switch 27 or possibly also by way of the logic of the control unit itself that the accumulator 26 is full and a 1 i -11further pressure reduction in the wheel brake cylinder 12 should take place, the return pump 28 must suck brake fluid out of the accumulator 26. For this reason, the return pump 28 is self-priming. In order for this to happen, the shut-off valves 16 and 17 must however be closed and the regulating valve 13 open. Also, the reduction valve 25 must be closed and the build-up valve 29 open. Following this switching operation, the desired reduction in volume in the accumulator 26 may take place. If the wheel brake cylinder 11 of the left-hand front wheel requires a pressure build-up during this time, it must wait until the reduction is terminated.

The pressure build-up in the wheel brake cylinder 11 of the left-hand front wheel may alo be carried out by the return pump 28 itself. To do this, the shut-off valve 16 is opened, the shut-off valve 17 for the wheel brake cylinder 12 of the right-hand front wheel is closed. Again, the reduction valve 25 is closed and the build-up valve 29 is opened. The wheel brake cylinder 11 can then be subjected to brake fluid by way of the return line 30 and the branch line 14.

If the volume of the accumulator 26 is not sufficient for a build-up, this is recognised by way of the control logic or possibly once again by way of the switch 27. and the regulating valve 13 is opened.

Brake pressure is then once again applied through the master brake cylinder 1.

It is advantageous in this case that the brake pedal remains stationary as long as the volume in the accumulator 26 is sufficient for a pressure modulation. As a result, a reduced pedal reactive effect takes place and noise is reduced, since the return pump only delivers against the pressure in the wheel brake cylinders and not against the pressure in the master brake cylinder. The pressure in the wheel brake cylinders may be reduced to 0 bar, since the accumulator 26 or the accumulator piston 37 provided in it is not spring-loaded.

In the embodiment of the braking system as in Fig. 2, the return pumps 28 and 35 are not selfpriming; rather the piston 37 of the accumulator 26a or 33a is under the pressure of a spring 38. As a result, brake fluid volume is pressed out of the accumulator 26a or 33a, with the build-up valve 29 or 34 open, to the return pump 28 or 35. In order for there not to be a simultaneous displacement of brake fluid to the build-up valve 25a or 32a, corresponding non-return valves 39 and 40 are provided. Furthermore, in order to limit a pressure between the pump and the inlet valve (e.g. 16, 17), a bypass line 41 or 42 is provided directly in the line 30 or 30a -13beyond the return pump 28 or 35, in which is disposed a pressurelimiting valve 43 or 44.

Furthermore, the braking system as in Fig. 2 also differs from that in Fig. 1 in that the two wheel brake cylinders 5 and 6 of the rear axle are controllable separately. One shut-off valve 9a and 9b is prov.1ded for each wheel brake cylinder 5 and 6. Furthermore, two non-return valves 20a and 20b and two reduction valves 32a and 32b are also required in this case.

In the event of a desired pressure reduction, the volume of brake fluid from the wheel brake cylinders 5, 6, 11 or 12 is taken up directly by the accumulators 26a or 33a and at the same time however delivered to the intake side of the pump 28 or 35, in order to ensure that a pressure reduction to very low values (0.5-1 bar) is possible.

If, in the event of very low coefficients of friction of a road, a certain pedal reactive effect is to be accepted, the build-up valve 29 or 34 and the associated non-return valve 39 or 40 can be dispensed with. In order in the event of very low coefficients of friction to achieve small residual pressures in the wheel brake cylinders 5. 6 or 11. 12. the regulating valve 8a or 13a is open during pressure reduction.

In the event of an increase in the coefficient of friction of a road during the anti-skid operation, the volume in the accumulator 26a or 33a may become exhausted, as a result of which the pump pressure is the same as the pressure in the wheel brake cylinders. Since, in the present embodiment, the closed position of the regulating valves 8a or 13a is occupied by a non-return valve, brake fluid can flow out of the master brake cylinder 1. As soon as, on reduction in the coefficient of friction of the road, the capacity of the accumulator 26a or 33a is no longer sufficient, this is recognised by the switch 27 and the regulating valve 8a or 13a is opened again.

The outlay on a braking system is considerably reduced if, as indicated in Fig. 3, hydraulic multiplexing takes place on the front axle and selectlow takes place on the rear axle. In such case, the accumulator 26b or 33b is in the form of an active ABS accumulator. The accumulator piston 37 is disposed in it so as to be controllable, wherein the accumulator piston 37 may be displaced. This is effected by a magnetic, electromotive, hydraulic or similar drive. The accumulator piston 37 brings about a charging pressure for the return pump 28 or 35 and prevents the return pump delivering in the non-activated state. In the event of a desired pressure reduction, the -15reduction valve 25 or 32 is openedt the accumulator 26b or 33b is not activated. As a result, filling of the accumulator 26b or 33b takes place. Only in the event of a desired pressure build-up by way of the return pump 28 or 35 is the accumulator 26b or 33b activated, and brake fluid may flow by way of the return line 30 to the wheel brake cylinders.

By virtue of the multiplex method, as described, for example, in US-PS 4 416 347, no pressure build-up may take place at the wheels of the front axle at one wheel while pressure is still being reduced at the other wheel.

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Claims

-16CLAIMS

1. A braking system comprising a master brake cylinder connected by way of a master brake line to wheel brake cylinders, a regulating valve and, for the wheel brake cylinders, a shut-off valve, disposed in the master brake line for anti-skid control, wherein a line branches off from the master brake line beyond the regulating valve to an accumulatort to which is connected a return pump, which is connected by way of a return line to the master brake line also beyond the regulating valve.

2. A braking system as claimed in claim 1, wherein at least one reduction valve, which has an open and a closed position, is disposed in the branched line.

3. A braking system as claimed in claim 2, wherein the accumulator is an active accumulator.

4. A braking system as claimed in claim 3, wherein an accumulator piston can be subjected to pressure in the accumulator by way of a magnetic, electric, hydraulic or similar drive.

5. A braking system as claimed in claim 3 or claim 4, wherein in the event of a desired pressure reduction in the wheel brake cylinders, no activation of the accumulator takes place.

6. A braking system as claimed in claim 2, 1 -17wherein a build-up valve is provided between the accumulator and the return pump.

7. A braking system as claimed in claim 6, wherein the return pump is self-priraing.

8. A braking system as claimed in claim 6, wherein an accumulator piston in the accumulator is under the pressure of a spring.

9. A braking system as claimed in claim 8# wherein the accumulator is protected from the reducing valve by a non-return valve.

10. A braking system as claimed in claim 8 or 9, wherein a bypass, in which a pressure-limiting valve is disposed, is provided between the accumulator and the return line beyond the return pump.

11. A braking system as claimed in any of claims 8 to 10, wherein the closed position of the regulating valves is in the form of A non-return valve.

12. A braking system as claimed in any of claims 1 to 11, wherein a damping chamber is associated with the return line.

13. A braking system as claimed in any of the preceding claims, comprising a plurality of said master brake lines.

14. A braking system as claimed in any of the preceding claims, comprising a plurality of shut-off valves in a master brake line.

15. A braking system as claimed in claim 14, comprising a plurality of shut-off valves in each master brake line.

16. A braking system substantially as herein described, with reference to, and as illustrated in Fig.1, Fig.2, or Fig.3 of the accompanying drawings Z.

Published 11991 at The Patent Office. Concept House. CardifT Road. Newport- Gwent \FI9 1 RH Further copies may be obtained from Sales Branch Unit 6. Nine Mile Point. CA-mfelinfach Cross Kevs. Newport. NPI 7HZ. Printed by Multiple., techniques ltd. St Mary Cray. Kent.